Method of continuously vaporizing and superheating liquefied cryogenic fluid

ABSTRACT

The present invention relates to an improved method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated to a desired temperature level by exchange of heat with gas turbine exhaust gases. By the present invention, the vaporized cryogenic fluid is passed in heat exchange relationship with the turbine exhaust gases in successive serially connected heat exchange stages. A quantity of liquefied cryogenic fluid is combined with the vaporized cryogenic fluid passing through each of the stages so that the liquefied cryogenic fluid is vaporized and the resulting combined vapor is cooled prior to passing through the next successive heat exchange stage. By the present invention, smaller and less expensive heat exchange apparatus is required and the maximum heating capacity of the turbine exhaust gases is utilized for vaporizing and superheating the cryogenic fluid.

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Arenson METHOD OF CONTINUOUSLY VAPORIZING AND SUPERHEATING LIQUEFIEDCRYOGENIC FLUID Inventor: Edwin M. Arenson, El Reno, Okla.

Assignee: Black, Sivalls & Bryson Inc.,

Oklahoma City, Okla.

Filed: May 20, 1971 Appl. No.: 145,217

[52] U.S. Cl. ..62/52, 48/190, 60/3907, 60/3946, 62/53, 261/145 [51]Int. Cl ..Fl7c 7/02, F02m 31/00 [58] Field of Search ..62/52, 53;261/145; 48/190; 60/3946, 39.07

[56] References Cited UNITED STATES PATENTS 3,154,928 11/1964 Harmens,.62/53 3,438,216 4/1969 Smith ..62/52 3,552,134 1/1971 Arenson ..60/95R Primary ExaminerWilliam F. ODea Assistant ExaminerPeter D. FergusonAttorney-Dunlap, Laney, Hessin & Dougherty 5 7 ABSTRACT The presentinvention relates to an improved method of continuously vaporizing andsuperheating a stream of liquefied cryogenic fluid wherein the stream isvaporized and then superheated to a desired temperature level byexchange of heat with gas turbine exhaust gases. By the presentinvention, the vaporized cryogenic fluid is passed in heat exchangerelationship with the turbine exhaust gases in successive seriallyconnected heat exchange stages. A quantity of liquefied cryogenic fluidis combined with the vaporized cryogenic fluid passing through each ofthe stages so that the liquefied cryogenic fluid is vaporized and theresulting combined vapor is cooled prior to passing through the nextsuccessive heat exchange stage. By the present invention, smaller andless expensive heat exchange apparatus is required and the maximumheating capacity of the turbine exhaust gases is utilized for vaporizingand superheating the cryogenic fluid.

9 Claims, 2 Drawing Figures 54, ,/56 we I60 METHOD OF CONTINUOUSLYVAPORIZING AND SUPEREIEATING LIQUEFIED CRYOGENIC FLUID BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relatesgenerally to an improved method of continuously vaporizing andsuperheating liquefied cryogenic fluid, and more particularly, but notby way of limitation, to a method of vaporizing and superheating astream of liquefied cryogenic fluid wherein the fluid is heat exchangedwith turbine exhaust gases.

2. Description of the Prior Art Many various methods and systems havebeen developed for vaporizing and superheating cryogenic fluids. Theterm cryogenic fluid is used herein to mean those fluids which exist inthe liquid state at a temperature below about 150 F at pressures up toabout 1000 psia, e.g., liquefied natural gas.

In recent years the use of liquefied natural gas as a source of fuel inareas where natural gas is unavailable has increased. In these areas, acontinuous stream of liquefied natural gas is vaporized, superheated anddistributed by pipeline to points of use. Many various methods andsystems have been developed and used for vaporizing and superheatingliquefied cryogenic fluids.

Generally, the methods and systems have required elaborate heatingequipment involving high operating costs. Recently, in order to improvethe economics of such systems, it has been proposed to utilize ambientwater as the heating medium for vaporizing and superheating liquefiednatural gas. The term ambient water is used herein to mean watercontained in large bodies such as oceans, lakes, rivers, etc. Further,in order to vaporize and superheat a stream of liquefied cryogenic fluidutilizing ambient water without incurring a detrimental temperature dropin the ambient water and in order to generate power for pumping theliquefied cryogenic fluid and ambient water streams, a method utilizingambient water to vaporize the stream of liquefied cryogenic fluid andutilizing turbine exhaust gases for superheating the vaporized cryogenicfluid to a desired level of superheat was developed and is described inmy co-pending application Ser. No. 150,448 filed June 7, 1971. Whilemethods and systems utilizing ambient water and turbine exhaust gas heatexchange for vaporizing and superheating a liquefied cryogenic fluidstream are highly advantageou economically, in certain applicationsinadequate temperature control of the superheated cryogenic fluid streammay be experienced.

By the present invention an improved method of continuously vaporizingand superheating a stream of liquefied cryogenic fluid wherein thestream is vaporized and then superheated to a desired temperature levelby exchange of heat with gas turbine exhaust gases is provided whereinmaximum temperature control of the superheated cryogenic fluid isprovided and utilization of the maximum heating capacity of the turbineexhaust gases is achieved.

SUMMARY OF THE INVENTION The present invention relates to an improvedmethod of continuously vaporizing and superheating a stream of liquefiedcryogenic fluid wherein the stream is vaporized and then superheated toa desired temperature level by exchange of heat with gas turbine exhaustgases. By the present invention, the vaporized cryogenic fluid is passedin heat exchange relationship with the turbine exhaust gases insuccessive serially connected heat exchange stages. Quantities ofliquefied cryogenic fluid are combined with the vaporized cryogenicfluid passing through each of said stages so that the liquefiedcryogenic fluid is vaporized and the resulting combined vapor is cooledprior to passing through the next successive heat exchange stage therebyutilizing the maximum heating capacity of said turbine exhaust gases.

It is, therefore, a general object of the present invention to providean improved method of continuously vaporizing and superheating liquefiedcryogenic fluid.

A further object of the present invention is the provision of animproved method of vaporizing and superheating a liquefied cryogenicfluid stream wherein the cryogenic fluid stream is heated and vaporizedby exchange of heat with ambient water and then superheated to a desiredtemperature level by exchange of heat with turbine exhaust gases.

Yet a further object of the present invention is the provision of animproved method of vaporizing and superheating a stream of liquefiedcryogenic fluid by exchange of heat with turbine exhaust gases whereinsmaller and less expensive heat exchange apparatus is required and themaximum heating capacity of the turbine exhaust gases is utilized.

Other and further objects of the present invention will be apparent fromthe following detailed description of the presently preferredembodiments of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates, in diagrammaticform, one system which may be utilized for carrying out the improvedmethod of the present invention, and

FIG. 2 illustrates, in diagrammatic form, a preferred arrangement ofheat exchange and gas turbine apparatus for the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,and particularly to FIG. 1, one system which may be utilized forcarrying out the method of the present invention is illustrated indiagrammatic form, and generally designated by the numeral 10. A streamof liquefied cryogenic fluid from a conventional liquefied cryogenicfluid storage tank 12, or other source, is pumped by pump 14 into one ormore ambient water-cryogenic fluid heat exchangers 18 by way of conduit16. The heat exchangers 18 may be a plurality of conventional open rackwater heat exchangers or other conventional heat exchangers suitable foruse with large volumes of ambient water. A conduit 20 having one enddisposed beneath the surface of the ambient water source is connected toone or more conventional water pumps 22. The discharge of the pumps 22is connected by a conduit 24 to the water inlet connection of the heatexchangers 18. After passing through the exchangers 18, the water isreturned or recycled to its source by way of a conduit 26. As theliquefied cryogenic fluid stream passes through the heat exchangers 18,heat is exchanged between it and the water passing therethrough causingthe cryogenic fluid stream to be heated and vaporized. The volume ofwater passed through the exchangers 18 is controlled so that thetemperature drop in the water is maintained at a level meeting thermalpollution standards, e.g., 1 to 2 F.

A pair of conventional gas turbines 28 and 30 are provided, each ofwhich generates large volumes of hot exhaust gases through thecombustion of fuel and air. Two gas turbines are provided in order toinsure that one of the turbines is operable at all times and that acontinuous stream of vaporized and superheated natu ral gas is produced.However, as will be described further hereinbelow, both of the gasturbines 28 and 30 are continuously operated.

The exhaust gases generated by the gas turbine 28 are conducted by wayof a conduit or duct 32 to a heat exchanger 34. The cryogenic fluidstream heated and vaporized in the heat exchangers l8 exits theexchangers 18 by way of a conduit 36. The conduit 36 is connected to apair of conduits 38 and 40 and conventional controls are providedtherein (not shown) for dividing the vaporized cryogenic fluid streaminto two portions, the first portion passing into conduit 38 and thesecond portion passing into the conduit 40. The first portion passes byway of conduit 38 to a pair of conduits 42 and 44 and conventionalcontrols are provided (not shown) for dividing the first portion of thevaporized cryogenic fluid into two streams which pass through theconduits 42 and 44.

The stream of vaporized cryogenic fluid passing through the conduit 42is conducted to heating tubes disposed within the heat exchanger 34.While passing through the heating tubes within the exchanger 34, heat isexchanged between the turbine exhaust gases and the vaporized cryogenicfluid stream so that the cryogenic fluid stream is heated to apredetermined temperature level. In addition, as will be describedfurther hereinbelow, a quantity of liquefied cryogenic fluid is combinedwith the vaporized cryogenic fluid stream passing through the heatexchanger 34 so that the maximum heating capacity of the turbine exhaustgases is utilized. The superheated cryogenic fluid vapor exiting theheat exchanger 34 passes into a conduit 48 connected thereto.

The exhaust gases generated by the turbine 30 are conducted by way of aconduit or duct 50 to a heat exchanger 52. The stream of vaporizedcryogenic fluid passing through the conduit 44 is conducted to heatingtubes disposed within the heat exchanger 52. While passing through theexchanger 52, heat is exchanged between the turbine exhaust gases andthe vaporized cryogenic fluid stream so that the cryogenic fluid streamis heated to a predetermined level of superheat. As in the case of heatexchanger 34, a quantity of liquefied cryogenic fluid is combined withthe cryogenic fluid vapor passing through the heat exchanger 52 and theresultant superheated cryogenic fluid exits the heat exchanger 52 by wayof a conduit 56. The spent turbine exhaust gases exit the exchangers 34and 52 by way of conduits or ducts 58 and 60 from where the exhaustgases are vented to the atmosphere.

The second portion of the vaporized cryogenic fluid from the exchangers18 passes through the conduit 40 to a pair of conduits 62 and 64.Conventional controls are provided in the conduits 62 and 64 (not shown)for dividing the second portion of vaporized cryogenic fluid stream intotwo streams, one of which passes through the conduit 64 and the otherthrough the conduit 62. The stream of vaporized cryogenic fluid passingthrough the conduit 64 is conducted to a plurality of heating tubesdisposed within a heat exchanger 68. Combustion air for the turbine 28is drawn from the atmosphere by way of a conduit through the heatexchanger 68 and then by way of a conduit 72 into the gas turbine 28.While passing through the heat exchanger 68, heat is exchanged betweenthe stream of vaporized cryogenic fluid and the combustion air so thatthe combustion air is cooled. As has been heretofore known, the coolingof the combustion air utilized in the gas turbine 28 is advantageous inthat the power output of the turbine 28 is increased accordingly. Afterpassing through the heat exchanger 68 the vaporized cryogenic fluidstream is conducted by a conduit 74 to a conduit 76.

The stream of vaporized cryogenic fluid passing through the conduit 62is conducted to a plurality of heating tubes disposed within a heatexchanger 80. Combustion air is drawn from the atmosphere by way of aconduit 82 through the heat exchanger and then by way of the conduit 84to the gas turbine 30. The vaporized cryogenic fluid stream exiting theexchanger 80 is conducted by way of a conduit 86 to the conduit 76 whereit is combined with the stream of vaporized cryogenic fluid passingthrough the conduit 76 from the heat exchanger 68. As will be describedfurther herein, quantities of liquefied cryogenic fluid are combinedwith the vaporized cryogenic fluid streams passing through theexchangers 68 and 80 to prevent the formation of excessive quantities ofice in the exchangers. The combined vaporized cryogenic fluid stream isconducted by the conduit 76 to a conduit 88.

The conduits 48 and 56 connected to the heat exchangers 34 and 52respectively are connected to the conduit 88. Thus, the superheatedcryogenic fluid streams passing from the exchangers 34 and 52 arecombined in the conduit 88 with the stream of vaporized cryogenic fluidpassing thereto by way of conduit 76. From the conduit 88 the compositestream of vaporized and superheated cryogenic fluid is conducted by aconduit 90 to a vapor-liquid contactor 92. A stream of liquefiedcryogenic fluid is conducted to the contactor 92 by way of a conduit 94connected thereto and connected to the conduit 16. The quantity ofliquefied cryogenic fluid passed to the contactor 92 by way of theconduit 94 is controlled such that the resultant combined stream exitingthe contactor 92 by way of the conduit 96 is at a desired specifictemperature. That is, the contactor 92 is utilized to combine acontrolled quantity of liquefied cryogenic fluid with the stream ofsuperheated cryogenic fluid passing therethrough so that the combinedstream is produced at a desired temperature. Thus, in the event ofoperational fluctuations in the system 10 and load changes on theturbines 28 and 30, the temperature of the vaporized and superheatedcryogenic fluid stream produced is maintained at a constant level. Fromthe conduit 96 the vaporized and superheated cryogenic fluid isconducted to a point of use or distribution. Fuel for the gas turbines28 and 30 may be drawn from the composite vaporized and superheatedcryogenic fluid stream passing through the conduit 88 by way of aconduit 98 attached thereto.

Referring now to FIG. 2, a preferred arrangement of the gas turbines 28and 30 and heat exchangers 34, 52, 68 and 80 is illustrated.

As shown in FIG. 2, the stream of cryogenic fluid heated and vaporizedin the heat exchangers 18 is passed by way of conduit 36 to a-pair ofconduits 38 and 40. The conduit 40 leads a portion of the vaporizedcryogenic fluid to a pair of conduits 62 and 64. The conduit 64 leads astream of the cryogenic fluid vapor to the heat exchanger 68 associatedwith the gas turbine 28. As previously described, atmospheric air isdrawn through the heat exchanger 68 by way of the conduit 70 wherein itis cooled by heat exchange with the vaporized cryogenic fluid, and thenpassed by way of conduit 72 to the turbine 28. A conventionaltemperature controller 100 is disposed in the air conduit or duct 72.The temperature controller 100 senses the temperature of the input airto the turbine 28 and opens or closes a conventional control valve 102disposed in the conduit 64 accordingly. That is, if the temperature ofthe air passing through the conduit 72 is too high, the temperaturecontroller 100 opens the control valve 102 so that more cryogenic fluidvapor is passed through the heat exchanger 68 thereby providingadditional cooling to the air, and vice versa.

The heating tubes disposed within the heat exchanger 68 are arranged insuccessive serially connected stages. That is, a first bank of heatingtubes 104 is provided connected to the conduit 64. A second tube bank106 is provided connected externally of the exchanger 68 in series withthe tube bank 104 and a third tube bank 108 is connected externally ofthe exchanger 68 to the tube bank 106. The cryogenic fluid vapor streamexiting the heat exchanger 68 passes by way of conduit 74 into theconduit 76 as previously described. Shutoff valves 110 and 112 aredisposed in the conduits 64 and 74 respectively.

A quantity of liquefied cryogenic fluid is combined with the cryogenicfluid vapor stream passing through the tube bank 106 and a quantity ofliquefied cryogenic fluid is combined with the vapor stream passingthrough the tube bank 108 in order to cool the resulting combinedstreams prior to their passage through the tube banks. This stageinjection of liquefied cryogenic fluid is used to maintain thetemperature of the cryogenic fluid vapor stream passing through theexchanger 68 at a relatively constant level thereby preventing theformation of excessive ice on the outside surfaces of the heating tubes.This method of cooling the turbine combustion air is described in detailin my US. Pat. No. 3,552,134 dated Jan. 5, 1971.

As shown in FIG. 2, the liquefied cryogenic fluid combined in theexchanger 68 is conducted by way of a conduit 114 to a header 116. Theconduit 114 is connected to a source of liquefied cryogenic fluid whichmay be the conduit 16 downstream of the pump 14. A conduit 118 isconnected to the header 116 and to the outlet of the tube bank 104 ofthe exchanger 68. A conventional temperature control assembly 120 isdisposed in the conduit 118 for controlling the quantity of liquefiedcryogenic fluid injected. A block valve 122 is provided in the conduit118. A conduit 124 is connected to the header 116 and to the outlet ofthe tube bank 106. A temperature control assembly 126 and block valve128 are disposed in the conduit 124.

As will be apparent from FIG. 2, the heat exchanger 80. associated withthe gas turbine 30 is identical to the heat exchanger 68 describedabove. A portion of the cryogenic fluid vapor from the conduit 40 passesby way of the conduit 62 to the heat exchanger 80. A temperature controlvalve 132 disposed within the conduit 62 is operably connected to aconventional temperature controller 134 disposed in the air conduit orduct 84. Successive serially connected tube banks 130, 138 and 140 areprovided in the heat exchanger and a block valve 142 is disposed in theoutlet conduit 86 which is connected to the conduit 76. Conduits 144 and146 are provided connected to the liquefied cryogenic fluid header 116and to the tube banks and 138. Temperature control assemblies 148 and150 and block valves 152 and 154 are provided in the conduits 144 and146 respectively.

The portion of the vaporized cryogenic fluid passing through conduit 38is divided between the conduits 42 and 44 as previously described. Asshown in FIG. 2, the conduit 42 is connected to heating tubes disposedwithin the heat exchanger 34 associated with the turbine 28. The conduit44 is connected to heating tubes disposed within the heat exchanger 52associated with the turbine 30. As described above for the heat exchan'gers 68 and 80, each of the heat exchangers 34 and 52 include banks ofheating tubes arranged in successive serially connected stages. That is,the heat exchanger 34 includes three serially connected tube banks 156,158 and 160 and the heat exchanger 52 includes three serially connectedtube banks 166, 168 and 170. The conduit 42 is connected to the inlet ofthe tube bank 156 of the exchanger 34 and the outlet of the tube bank160 thereof is connected by the conduit 48 to the conduit 88. Theconduit 44 is connected to the inlet of the tube bank 166 of theexchanger 52 and the outlet of the tube bank 170 thereof is connected bythe conduit 56 to the conduit 88. Quantities of liquefied cryogenicfluid are injected or combined with the cryogenic fluid vapor passingthrough each stage or tube bank of each of the exchangers 34 and 52 sothat the resulting composite vapor streams are cooled and the maximumheating capacity of the exhaust gases passing through the heatexchangers 34 and 52 are utilized. For this purpose, a pair of conduits162 and 164 are connected to the header 116 and to the outlets of thetube banks 156 and 158 of the exchanger 34 and a pair of conduits 172and 174 connect the header 116 to the outlets of the tube banks 166 and168. Conventional temperature control assemblies 176 and 178 and blockvalves 180 and 182 are disposed in the conduits 162 and 164respectively. Similarly, conventional temperature controllers 184 and186 and block valves 188 and 190 are disposed in the conduits 172 and174 respectively. Shutofi or block valves 192, 194, 196 and 198 aredisposed in the conduits 42, 48 44 and 56 respectively.

The turbines 28 and 30 drive conventional electric generators 200 and202 respectively.

OPERATION OF THE SYSTEM 10 The system 10 includes two conventional gasturbines 28 and 30 which provide power for operating two conventionalelectric generators 200 and 202. The primary purpose of including twogas turbines and electric generators is to provide a standby turbine forproviding hot exhaust gases and electric power in the event one of theturbines fails thereby insuring the production of a continuous stream ofvaporized and superheated cryogenic fluid. However, in operation of thesystem 10, both of the gas turbines 28 and 30 are continuously operated.The electric power output of one of the electric generators 200 or 202is advantageously used for operating the liquefied cryogenic fluid pumps14 and the ambient water pumps 22. The electric power output from theother electric generator may be sold to a power company or otherelectric power consumer.

The system 10 is designed so that the required minimum rate of vaporizedand superheated cryogenic fluid may be produced utilizing the exhaustgases generated from one of the turbines 28 and 30. Thus, if one of theturbines fails and is taken out of service, the exhaust gases generatedby the other turbine are used to vaporize and superheat the requiredminimum rate of cryogenic fluid and the power output of the electricgenerator associated therewith is utilized to operate the pumps 14 and22.

During normal operation of the system 10, a stream of liquefiedcryogenic fluid is pumped by the pump 14 through the ambient watercryogenic fluid heat exchangers 18 by way of conduit 16. While passingthrough the exchangers 18 the stream of cryogenic fluid is heated andvaporized. As described above, the vaporized stream is split into twoportions, the major portion of which passes by way of conduit 38 to theconduits 42 and 44 where it is divided into two portions, one portionpassing by way of conduit 42 through the heat exchanger 34 and the otherportion passing by way of conduit 44 through the heat exchanger 52.While passing through the exchangers 34 and 52 the vaporized cryogenicfluid streams are combined with quantities of liquefied cryogenic fluidand the combined streams are superheated to desired temperature levels.The superheated streams then pass by way of conduits 48 and 56 into theconduit 88. The particular quantities of liquefied cryogenic fluidinjected in the heat exchangers 34 and 52 is controlled by thetemperature control assemblies 176, 178, 184 and 186. That is, thetemperature controllers 176 and 178 associated with the heat exchanger34 are set so that the temperature of the combined stream exiting theexchanger by way of conduit 48 is at a desired level, and thecontrollers 184 and 186 associated with the exchanger 52 are setsimilarly. Thus, during normal operation of the system 10, the heatexchangers 34 and 52 are each handling one-half the stream of cryogenicfluid heated and vaporized in the ambient water exchangers 18. In orderto utilize the full heating capacity of the exhaust gases produced bythe turbines 28 and 30, liquefied cryogenic fluid is injected into theexchangers 34 and 52.

The minor portion of the vaporized cryogenic fluid stream from theexchangers 18 passes by way of conduit 40 to the conduits 62 and 64wherein it is divided into two portions, one of which passes through theheat exchanger 68 and the other through the heat exchanger 80. Asdescribed above, the heat exchangers 68 and cool the input combustionair to the turbines 28 and 30 respectively. The heated combinedvaporized cryogenic fluid streams exiting the exchangers 68 and 80 arecombined in the conduit 76 and conducted to the conduit 88 where theycombine with the superheated cryogenic fluid streams from the exchangers34 and 52. The composite stream is conducted by conduit 90 to thecontactor 92 wherein a small additional quantity of liquefied cryogenicfluid is combined with the composite stream to trim out the temperatureof the stream. From the contactor 92, the stream is conducted to a pointof use or distribution.

As shown in FIG. 2, the portion of vaporized cryogenic fluid from theexchangers 18 which is routed to the combustion air coolers 68 and 80 iscontrolled by the temperature controllers and 134 and control valves 102and 132. That is, the quantity of vaporized cryogenic fluid passed tothe exchangers 68 and 80 is increased or decreased by the temperaturecontrollers 100 and 102 in accordance with the temperatures of thecombustion air streams passing to the turbines 28 and 30. The remainingportion of the vaporized cryogenic fluid stream is divided substantiallyequally between conduits 42 and 44. The division of the stream may beaccomplished through the utilization of con-. ventional flow controllers43 and 45 disposed in the conduits 42 and 44. As will be understood bythose skilled in the art, many various other control apparatus may beused for dividing the vaporized cryogenic fluid stream exiting the heatexchangers 18 into the various portions required.

In the event one of the turbines 28 or 30 either fails or must be shutdown for other reasons, the required minimum rate of vaporized andsuperheated cryogenic fluid is produced by the system 10. Specifically,let it be assumed that the turbine 28 is shut down. Upon shut down ofthe turbine 28, the block valves disposed in the conduits to and fromthe heat exchangers 68 and 34 are closed. That is, the valves 110, 112,122 and 128 associated with the exchanger 68 are closed, and the valves180, 182, 192 and 194 associated with the exchanger 34 are closed.Additionally, the flow of liquefied cryogenic fluid to the exchanger 52by way of the conduits 172 and 174 is reduced or stopped. Thus, inoperation of the system 10 with the turbine 28 and relating heatexchangers shut down, the stream of vaporized cryogenic fluid exitingthe ambient water heat exchangers 18 passes by way of the conduit 36 tothe conduit 38 and 40. A minor portion of the vaporized cryogenic fluidstream passes by way of the conduit 40 to the heat exchanger 80 whereinit is utilized to cool the input combustion air to the turbine 30 in thesame manner as described above. The major portion of the vaporizedcryogenic fluid passes by way of conduit 38 to the heat exchanger 52. Asthe vaporized cryogenic fluid stream passes through the exchanger 52 itis superheated to as high a temperature as possible without the additionof liquefied cryogenic fluid. Normally, the system 10, and specificallythe heat exchangers 34 and 52 are designed so that when the entiresuperheating load is handled by one of the exchangers 34 or 52, thestream of cryogenic fluid is heated to a temperature only slightlyhigher than the desired temperature. In order to trim out thetemperature, i.e., reduce the temperature of the cryogenic fluid streamto a desired level and allow for operational fluctuations and loadchanges, the stream is passed to the contactor 92 (FIG. 1) wherein aquantity of liquefied cryogenic fluid is combined therewith as describedabove. The quantity of liquefied cryogenic fluid combined in thecontactor 92 is controlled by conventional temperature controlinstruments (not shown) so that the resulting com bined stream exitingthe contactor 92 by way of the conduit 96 is at the desired temperature.

Thus, by the present invention, both of the turbines 28 and 30 arecontinuously operated with the maximum heating capacity of the turbineexhaust gases being utilized to vaporize and superheat cryogenic fluid.Further, the electric power output of the generators associated with theturbines is utilized to operate the various pumps of the system 10, witha portion thereof being sold to an outside consumer or otherwiseutilized. In the event of a turbine shut down, the

required vaporized and superheated cryogenic fluid 1 rate is produced bythe system 10.

As will be understood, the present invention wherein controlledquantities of liquefied cryogenic fluid are stage combined with avaporized cryogenic fluid stream being superheated by exchange of heatwith turbine exhaust gases is not limited to use in the specific systemdescribed above and may be utilized to advantage in a variety ofsystems. By the use of the present invention, the surface area requiredfor the turbine exhaust gas heat exchanger is reduced due to theresulting higher log mean temperature difference achieved.

in order to present a clear understanding of the present invention, thefollowing example is given:

EXAMPLE Let it be assumed that the system 10 must be capable ofproducing a 929 mmscf/day stream of natural gas at a temperature of 60F. During normal operation, a 1,496,500 lb/hr stream of liquefiednatural gas (LNG) at a temperature of 260 F is pumped from the storagetank 12 by the pump 14 to the heat exchangers 18 at a pump dischargepressure of 1000 psig. A 476,000 gpm stream of ambient water at atemperature of 70 F is pumped by the pumps 22 through the heatexchangers 18. For a 2 temperature drop in the water, 476,380,000 btu/hrare transferred from the ambient water stream to the LNG stream causingthe LNG to be vaporized and heated to a temperature of 0 F. Thevaporized natural gas stream at a temperature of 0 F is conducted by theconduit 36 to the conduits 38 and 40. AS88560 lb/hr portion of thenatural gas is passed by way of conduit 40 to the conduits 62 and 66. A294,280 lb/hr stream is passed by way of the conduit 64 through theheating tubes disposed within the heat exchanger 68, and a 294,280 lb/hrstream is passed by way of the conduit 62 through the heating tubesdisposed in the heat exchanger 80. Each of the exchangers 68 and 80 areoperated in an identical manner. That is, a 767,800 lb/hr stream ofcombustion air at a temperature of 80 F (50 percent saturated withwater) is drawn through the conduits 70 and 82 to the exchangers 68 and80 respectively. As the combustion air stream is passed through the heatexchangers 68*and 80, 12,190,000 btu/hr of heat is transferred from theair to the natural gas streams, causing the air to be cooled to atemperature of 40 F. 35,456 lb/hr of LNG are combined with the naturalgas passing through the heat exchangers 68 and 80. That is, 35,456 lb/hrof LNG are combined with the natural gas passing through the tube banks104, 106 and 108 of the exchanger 68 and a 329,736 lb/hr combined streamof natural gas exits the heat exchanger 68 at a temperature of 3 F.35,456 lb/hr of LNG are combined with the natural gas stream passingthrough the tube banks 130, 138 and 140 of the exchanger and a 329,736lb/hr combined stream of natural gas exits the heat exchanger 80 at atemperature of 3 F. The natural gas streams from the exchangers 68 and80 are combined and a 659,472 lb/hr stream of natural gas at atemperature of 3 F passes by way of the conduit 76 to the conduit 88.

A 907,940 lb/hr portion of the natural gas stream exiting the exchangers18 at a temperature of 0 F passes by way of the conduit 38 to theconduits 42 and 44. 453,970 lb/hr of the natural gas passes by way ofconduit 42 through the exchanger 34. 220,878 lb/hr of LNG are combinedwith the natural gas in the exchanger 34, which LNG is vaporized and theresulting combined stream (674,848 lb/hr) is heated to a temperature of150 F.

453,970 lb/hr of the natural gas at 0 F is passed by way of the conduit44 through the heat exchanger 52. 220,878 lb/hr of LNG are combined withthe natural gas in the heat exchanger 52 and the resulting combinedstream of 674,848 lb/hr exits the exchanger 52 at a temperature of 150F.

A 780,000 lb/hr stream of exhaust gases at a temperature of 950 F isproduced by each of the turbines 28 and 30. The exhaust gases areconducted from the turbines 28 and 30 by the ducts 32 and 50respectively to the exchangers 34 and 52. 133,000,000 btu/hr aretransferred from the turbine exhaust gases to the natural gas stream andinjected LNG, and the spent exhaust gases exit the exchangers 34 and 52at temperatures of 300 F. The superheated natural gas streams from theexchangers 34 and 52 pass by way of the conduits 68 and 56 respectivelyinto the conduit 88 where they combine with the natural gas streamentering the conduit 88 by way of the conduit 76. The resultantcomposite stream (2,009,168 lb/hr) at a temperature of 100 F isconducted by way of the conduit to the contactor 92. 135,016 lb/hr ofliquefied natural gas is conducted to the contactor 92 by way of theconduit 94 and the resultant natural gas stream exits the system 10 at arate of l,l46,000,000 scf/day and a temperature of 60 F by way of theconduit 89.

In operation of the system 10 with one of the turbines 28 or 30 shutdown, for example, with the turbine 28 shut down, the natural gas streamexiting the exchangers 18 at a temperature of 0 F is divided into majorand minor portions, the minor portion (294,280 lb/hr) passing by way ofthe conduits 40 and 62 to the heat exchanger 80. A 329,736 lb/hr streamof natural gas exists the exchanger 80 by way of the conduits 86 and 76at a temperature of 3 F. The major portion of the natural gas stream(1,202,220 lb/hr) at a temperature of 0 F passes by way of the conduits38 and 44 to the turbine exhaust gas heat exchanger 52 associated withthe turbine 30. While passing through the heat exchanger 52, 133,000,000btu/hr is transferred from the turbine exhaust gases to the natural gasstream causing the natural gas stream to be superheated to a temperatureof 175 F. Spent turbine exhaust gases at a temperature of 300 F areconducted from the exchanger 52 by way of duct 60. The superheatednatural gas stream from the exchanger 52 passes by way of the conduit 56to the conduit 88 wherein it is combined with the natural gas passinginto the conduit 88 by way of the conduit 76 making a total compositestream of 1,531,956 lb/hr at a temperature of 140 F. The compositestream is passed from the conduit 88 by way of the conduit 90 to thecontactor 92. A 205,971 lb/hr LNG stream is passed by way of the conduit94 to the contactor 92 wherein it intimately mixes with the natural gasstream. While within the contactor 92, heat is transferred from thesuperheated natural gas stream to the LNG stream causing the LNG to bevaporized and combined with the natural gas stream resulting in a 929mmscf/day stream of natural gas at a temperature of 60 F.

The present invention, therefore, is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thoseinherent therein. While presently preferred systems for carrying out themethod of the present invention are given for the purpose of disclosure,numerous changes can be made which will readily suggest themselves tothose skilled in the art and which are encompassed within the spirit ofthe invention disclosed herein.

What is claimed is:

1. In a method of continuously vaporizing and superheating a stream ofliquefied cryogenic fluid wherein the stream is vaporized and thensuperheated to a desired temperature level by exchange of heat with gasturbine exhaust gases, the improvement comprising:

passing said vaporized cryogenic fluid in heat exchange relationshipwith said turbine exhaust gases in successive serially connected heatexchange stages; and

combining a quantity of liquefied cryogenic fluid with the vaporizedcryogenic fluid passing through each of said stages so that theliquefied cryogenic fluid is vaporized and the resulting combined vaporis cooled prior to passing through the heat exchange stage therebyutilizing the maximum heating capacity of said turbine exhaust gases.

2. The method of claim 1 wherein the liquefied cryogenic fluid isliquefied natural gas.

3. In a method of continuously vaporizing a stream of liquefiedcryogenic fluid wherein the stream is vaporized and then superheated byexchange of heat with gas turbine exhaust gases, at least a portion ofthe vaporized cryogenic fluid stream being passed in heat exchangerelationship with the turbine input air so that said air is cooled andthe power output of the turbine increased, the improvement comprising:

dividing said stream of liquefied cryogenic fluid into first and secondstreams;

passing said first stream of liquefied cryogenic fluid in heat exchangerelationship with a stream of ambient water so that said first stream isheated and vaporized;

passing said heated and vaporized stream in heat exchange relationshipwith said turbine exhaust gases in successive serially connected heatexchange stages; and

4. The method of claim 3 which is further characterized to include thesteps of:

passing the portion of the vaporized cryogenic fluid stream heatexchanged with said turbine input air in successive serially connectedheat exchange stages with said air; and

combining a portion of said second stream of liquefied cryogenic fluidwith the vaporized cryogenic fluid passing through each of saidinput airheat exchange stages so that the resulting combined stream is cooledprior to passing through the stage thereby maintaining the formation ofice from water vapor contained in said air at a minimum.

5. The method of claim 4 wherein the liquefied cryogenic fluid isliquefied natural gas.

6. The method of claim 5 wherein a portion of the produced vaporized andsuperheated natural gas is utilized as fuel for said turbine.

7. In a method of continuously vaporizing a stream of liquefiedcryogenic fluid wherein the stream is vaporized and then superheated byexchange of heat with gas turbine exhaust gases, at least a portion ofthe vaporized cryogenic fluid stream being passed in heat exchangerelationship with the turbine input air so that said air is cooled andthe power output of the turbine increased, the improvement comprising:

a. dividing said stream of liquefied cryogenic fluid into first, secondand third streams;

b. passing said first stream of liquefied cryogenic fluid in heatexchange relationship with a stream of ambient water so that said firststream is heated and vaporized;

c. passing said heated and vaporized stream in heat exchangerelationship with said turbine exhaust gases in successive seriallyconnected heat exchange stages;

d. combining portions of said second stream of liquefied cryogenic fluidwith the vaporized cryogenic fluid passing through each of said turbineexhaust gases heat exchange stages so that the liquefied cryogenic fluidis vaporized and the resulting combined stream is cooled prior topassing through the stage thereby utilizing the maximum heating capacityof said turbine exhaust gases; and

. combining said third stream of liquefied cryogenic fluid with thestream of heated and vaporized cryogenic fluid from step (d) so that theresultant composite vapor stream is produced at a desired temperature.

8. The method of claim 7 which is further characterized to include thesteps of:

passing the portion of the vaporized cryogenic fluid stream heatexchanged with said turbine input air in successive serially connectedheat exchange stages with said air; and

from water vapor contained in said air at a minimum. 9. The method ofclaim 8 wherein the liquefied cryogenic fluid is liquefied natural gas.

2. The method of claim 1 wherein the liquefied cryogenic fluid isliquefied natural gas.
 3. In a method of continuously vaporizing astream of liquefied cryogenic fluid wherein the stream is vaporized andthen superheated by exchange of heat with gas turbine exhaust gases, atleast a portion of the vaporized cryogenic fluid stream being passed inheat exchange relationship with the turbine input air so that said airis cooled and the power output of the turbine increased, the improvementcomprising: dividing said stream of liquefied cryogenic fluid into firstand second streams; passing said first stream of liquefied cryogenicfluid in heat exchange relationship with a stream of ambient water sothat said first stream is heated and vaporized; passing said heated andvaporized stream in heat exchange relationship with said turbine exhaustgases in successive serially connected heat exchange stages; andcombining portions of said second stream of liquefied cryogenic fluidwith the vaporized cryogenic fluid passing through each of said turbineexhaust gases heat exchange stages so that the liquefied cryogenic fluidis vaporized and the resulting combined stream is cooled prior topassing through the stage thereby utilizing the maximum heating capacityof said turbine exhaust gases to heat the combined stream to a desiredlevel of superheat.
 4. The method of claim 3 which is furthercharacterized to include the steps of: passing the portion of thevaporized cryogenic fluid stream heat exchanged with said turbine inputair in successive serially connected heat exchange stages with said air;and combining a portion of said second stream of liquefied cryogenicfluid with the vaporized cryogenic fluid passing through each of saidinput air heat exchange stages so that the resulting combined stream iscooled prior to passing through the stage thereby maintaining theformation of ice from water vapor contained in said air at a minimum. 5.The method of claim 4 wherein the liquefied cryogenic fluid is liquefiednatural gas.
 6. The method of claim 5 wherein a portion of the producedvaporized and superheated natural gas is utilized as fuel for saidturbine.
 7. In a method of continuously vaporizing a stream of liquefiedcryogenic fluid wherein the stream is vaporized and then superheated byexchange of heat with gas turbine exhaust gases, at least a Portion ofthe vaporized cryogenic fluid stream being passed in heat exchangerelationship with the turbine input air so that said air is cooled andthe power output of the turbine increased, the improvement comprising:a. dividing said stream of liquefied cryogenic fluid into first, secondand third streams; b. passing said first stream of liquefied cryogenicfluid in heat exchange relationship with a stream of ambient water sothat said first stream is heated and vaporized; c. passing said heatedand vaporized stream in heat exchange relationship with said turbineexhaust gases in successive serially connected heat exchange stages; d.combining portions of said second stream of liquefied cryogenic fluidwith the vaporized cryogenic fluid passing through each of said turbineexhaust gases heat exchange stages so that the liquefied cryogenic fluidis vaporized and the resulting combined stream is cooled prior topassing through the stage thereby utilizing the maximum heating capacityof said turbine exhaust gases; and e. combining said third stream ofliquefied cryogenic fluid with the stream of heated and vaporizedcryogenic fluid from step (d) so that the resultant composite vaporstream is produced at a desired temperature.
 8. The method of claim 7which is further characterized to include the steps of: passing theportion of the vaporized cryogenic fluid stream heat exchanged with saidturbine input air in successive serially connected heat exchange stageswith said air; and combining a portion of said second stream ofliquefied cryogenic fluid with the vaporized cryogenic fluid passingthrough each of said input air heat exchange stages so that theresulting combined stream is cooled prior to passing through the stagethereby maintaining the formation of ice from water vapor contained insaid air at a minimum.
 9. The method of claim 8 wherein the liquefiedcryogenic fluid is liquefied natural gas.